1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly, to an image forming apparatus including a current detection circuit for detecting the amount of a current that flows into the image forming apparatus from a commercial power supply.
2. Description of the Related Art
A laser printer, which is an image forming apparatus employing an electrophotographic process, includes: a latent image bearing member for bearing a latent image; a developing device for visualizing the latent image as a toner image by applying developer (hereinafter, referred to as toner) to the latent image bearing member; a transfer device for transferring the toner image onto recording paper conveyed in a predetermined direction; and a fixing device for fixing the toner image onto the recording paper by heating and pressurizing, under a predetermined fixing process condition, the recording paper that the toner image has been transferred onto by the transfer device.
With the recent speed-up of image forming apparatus, motors used in the image forming apparatuses have become faster/larger, resulting in increased consumption of current for the image forming apparatuses. Further, with the development of colorization of office documents, a large number of color laser printers have been produced. The color laser printer employs a large number of motors in order to perform multiple image formations simultaneously. In addition, due to the need to fix onto the recording paper the toner image that has multiple colors overprinted, the fixing device consumes a large amount of current. Further, with image forming apparatuses becoming more sophisticated, image forming apparatuses have come to be provided with option devices, such as a sheet feed option device for accommodating multiple sizes of recording paper, a sheet discharge option device for sorting or stapling delivered recording paper for every predetermined number of sheets, and an image scanner provided with an auto sheet feeder for performing copying or electronic filing of an original. As a result, the consumption current of the image forming apparatus is more and more increasing.
A guide for the upper limit of a current that is consumable in those apparatuses is specified by the Underwriters Laboratories Inc. (UL) standard in the U.S., the Electrical Appliance and Material Safety Law in Japan, or the like. Accordingly, the image forming apparatus needs to be so designed that the upper limit does not exceed the maximum current, which is suppliable by the commercial power supply. The maximum current is, for example, 15 A in Japan and the U.S., and is 10 A in the European Union (EU). Those figures are both root mean square values.
Normally, power consumed in the image forming apparatus becomes the highest during a period (warm-up period) where the fixing device is heated up until a fixable temperature. This is because, if loads other than the fixing device start print preparation operations during the warm-up period, a large amount of power that is being consumed in the fixing device is added with the consumption power of the other loads.
Hence, conventionally, in order to prevent the maximum current of the entire image forming apparatus from exceeding 15 A, designed has been such a sequence as to restrict the current flowing into the fixing device at a timing of activation of the loads other than the fixing device. For example, upon outputting activation signals to the loads other than the fixing device, the CPU also outputs a signal for restricting an input current to a temperature control portion of the fixing device.
On the other hand, because the consumption power of the fixing device in a printing period is not so high as in the warm-up period, it has been rare for the maximum current of the entire image forming apparatus to exceed 15 A, even if the loads other than the fixing device are activated while the current is flowing in the fixing device.
However, with the speed-up/upsizing of the employed motors, resulting from the speed-up of the image forming apparatus, as well as with the colorization, resulting from the increased number of the employed motors, the consumption power of the loads other than the fixing device has been increasing. Accordingly, there has been the need to carry out a design taking into account a situation where the maximum current of the entire image forming apparatus exceeds 15 A, even in the printing period.
Therefore, for the printing period, similarly to the warm-up period, it is conceivable to design such a sequence as to restrict the current flowing into the fixing device at the timing of activation of the loads other than the fixing device in order to prevent the maximum current of the entire image forming apparatus from exceeding 15 A.
However, each of the loads has a different activation timing from one another, making it extremely difficult to design a sequence that restricts the current flowing into the fixing device at each of the timings of activation of a large number of loads other than the fixing device. In addition, the consumption power of each of the loads other than the fixing device is not necessarily constant, but will fluctuate. Consequently, if the current flowing into the fixing device is restricted with a fixed rate upon activation of the loads other than the fixing device, there is a possibility that the current flowing into the fixing device is unnecessarily restricted, though there is room for the current to be used in the entire image forming apparatus. In such a case, the processing performance of the fixing device declines unnecessarily, eventually causing the processing performance of the image forming apparatus to decline unnecessarily.
Hence, Patent Document 1 discloses restricting, by providing a current detection device for detecting an input current into the image forming apparatus, a current flowing into the fixing device so as to prevent the current from exceeding the maximum current of the commercial power supply.
Patent Document 1 Japanese Patent Application Publication No. H03-073870